Radio receiver



Feb. 23, 1960 w. E. DENK 2,926,245

RADIO RECEIVER Filed ma 14, 1956 f/G/VAL (WAN/VIZ 0/ 440/0 RICE/Vi? IN V EN TOR.

W/ZZ/AM 1 05AM BY mml nih United States Patent ce RADIO RECEIVER William E. Denk, Devon, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application May 14, 1956, Serial No. 584,822

1 Claim. (Cl. 250-27) This invention relates to radio receivers employing electron tubes, and more particularly, the invention relates to on-otf control of such radio receivers.

In the conventional radio receiver, the opening of the on-off switch causes an abrupt cessation of the sound output of the receiver. This may be highly objectionable in some instances. For example, where a person has gone to sleep with a clock-controlled radio receiver operating in its delayed ofi condition, the abrupt cessation of sound, when the receiver shuts ofi at the predetermined time, is apt to awaken the sleeper. Thus the therapeutic value of the radio receiver as a sleep-inducing instrumentality is lost.

Most of the present day radio receivers employ electron tubes having indirectly heated cathodes. In the conventional radio receiver, the on-ofi switch is included both in the energizing circuit for the cathode heaters and in the rectifier circuit which supplies operating voltage for the tubes. When the on-off switch is opened in such a receiver, the tubes are rendered immediately inoperae tive due to the opening of said circuits, and consequently the sound output of the receiver ceases abruptly.

One object of the present invention is to overcome the above-mentioned objection and to provide an arrange ment by which cessation of the sound output of a radio receiver is caused to take place gradually, over a sub stantial period of time, when the on-oif switch is opened.

Another object of the invention is to provide such an arrangement in a clock-controlled radio receiver, wherein abrupt cessation of sound is particularly objectionable.

A further object of the invention, in its preferred form, is to provide a simple arrangement for the above-stated purpose which does not require any additional parts and does not increase the cost of the radio receiver.

It is characteristic of an electron tube having an indirectly heated cathode that the cathode has considerable thermal inertia. In accordance with the present invention, advantage is taken of this inherent characteristic of such tubes, and provision is made for maintaining the tubes of a radio receiver operative after the heater circuit for the tubes has been opened by the onoff switch. Preferably this result is achieved by arranging the on-otf switch so that it is included only in the energizing circuit for the cathode heaters. With this arrangement, when the on-ofi switch is opened, the current flow to the cathode heaters is interrupted, but the AC. input to the rectifier circuit is not interrupted, and therefore the tubes are not immediately rendered inoperative. Due to the thermal inertia of the cathodes, plates current in the tubes does not cease abruptly but decreases gradually, and the radio receiver continues to operate for a substantial period of time, e.-g., 15 to 30 seconds. During this time, the volume level of the sound gradually tapers ofi as the temperature of the tube cathodes decreases and the electron emission decreases accordingly.

The invention may be fully understood from the following detailed description with reference to the accompanying drawing wherein the single figure is a simplified diagrammatic illustration of a clock-controlled radio receiver employing electron tubes having indirectly heated cathodes and embodying the present invention.

Referring more particularly to the drawing, the signal channel of a conventional clock-controlled radio receiver is represented by the rectangle 1. The usual antenna is represented at 2, and the usual sound reproducer or loud speaker is represented at 3. The signal channel 1 includes a number of vacuum tubes having indirectly heated cathodes. Four such tubes are shown at 4, 5, 6 and 7, the number of tubes being chosen arbitrarily for the purpose of illustration. The tubes are shown as triodes, but it will be understood that the radio receiver may employ other types of tubes such as tetrodes or pentodes. Since this invention is not concerned with any of the other components of the signal channel of the radio receiver, there is no need for illustration of such other components.

The usual energy input conductors for the radio receiver are shown at 8 and 9, these conductors being connected to a conventional plug 10 by which they are connectable to a source of electrical energy. Operating voltages for the plate circuits of the tubes of the signal channel 1 are provided by means of the rectifier circuit which is connected to the energy input conductors 8 and 9, and which includes the rectifier tube 11, filter resistors 12 and 13, and filter capacitors 14, 15 and 16. In the arrangement shown, voltages B[ and B++ appear on conductors 17 and 18, and these voltages are applied to the anode circuits of the tubes in the signal channel 1 in conventional manner.

The heater energizing circuit is also connected to the energy input conductors 8 and 9, this circuit being designated generally by reference numeral 19. This circuit includes in series the heater elements of the various tubes.

As thus far described the radio receiver is conventional. In the past, the on-oif switch was located in the system (typically at point X) so as to be included in both the energizing circuit for the cathode heaters and the rectifying circuit which supplies the operating voltage for the tubes. Consequently, as previously mentioned, opening of the on-off switch caused abrupt termination of the operation of the receiver, and thus caused abrupt cessation of the sound output. The Philco clockradio model C734-124 is typical of such prior conventional radio receivers.

In accordance with this invention, the on-oif switch 20 is located in the system so that it is included only in the energizing circuit for the cathode heaters, being excluded from the rectifying circuit. It will be understood that the illustrated location of the switch 20 is merely one of various possible locations according to this invention. Other points at which the switch 20 may alternatively be placed are designated by the letter Y.

In the receiver illustrated, the on-otf switch 20 is controlled in conventional manner by the clock 21 which is connected to the supply conductors 8 and 9 ahead of switch 20. The usual delayed-off control knob is shown at 22, the setting of which determines the time of opening of the switch 20.

With the on-ofi' switch included only in the energizing circuit for the cathode heaters, opening of the switch interrupts the current flow through the heater elements but does not interrupt the rectifying circuit which supplies operating voltage for the tubes. Consequently the radio receiver continues to operate for a time interval determined by the thermal inertia of the indirectly heated cathodes of the tubes. As the temperature of the cathodes decreases, the electron emission in the tubes de- Patented Feb. 23, 1960 creases accordingly, and the volume level of the sound output decreases gradually to the point of cessation. Thus this invention eliminates the objectionable abrupt essatisa i thescilnd ou ut the rediq rsssi e r @92 au es the sound o tap b it a Plea i and 11. 0??- we adsqu This invention is. applicable, in general, to radio receivers employing conventional indirectly heated cathodes. Such cathodes may comprise an oxide-coated hollow nickel cylinder supported on, and in good heateirchange relation with, a cylindrical refractory body which is heated from within by a tungsten heater Wire. More recently indirectly heated cathodes have comprised an oxide coated hollow nickel cylinder heated from within by an Alundum (aluminum oxide) coated tungsten heater wire folded to make a number of passes through the nickel cylinder. Regardless of the specific construction employed, it has been noted that the overall mass of snch cathode and heater assemblies is such as to provide substantial thermal inertia which, as hereinbefore described, is made to serve the purpose of the present invention. Directly heated, i.e., filamentary type, cathodes do not possess sufiicient thermal inertia to be useful for the purpose of this invention.

In the system illustrated, the rectifier tube 11 is a diode having an indirectly heated cathode. This is advantageous in a system embodying the present invention, for the reason that it causes the operating voltage for the tubes to decrease as the temperature of the cathodes decreases. Thus as the electron emission in the rectitier tube 11 decreases, the voltages B+ and B++ decrease accordingly.

While a particular embodiment of the invention has been illustrated and described, the invention is not limited thereto but contemplates such modifications and other embodiments as may occur to those skilled in the n.

l e m A clock-controlled radio receiver adapted for auto.- matic turn-off at the end of a time interval pre-set by the user, wherein it is desired to effect gradual automatic turn-off so that the cessation ofsound will be gradual and not abrupt, said receiver comprising a signal channel including a plurality of vacuum tubes each having an anode, a cathode heater and an indirectly heated cathode having considerable thermal inertia which causes gradual cooling of the cathode upon cessation of heat supplied thereto, a pair of energy input conductors connectable to a source of electrical energy, an anode voltage supply circuit permanently connected to said conductors for supplying operating voltage to the anodes of said tubes, a cathode heater circuit connected to said conductors and includingv the cathode heaters of said tubes, a receiver turn-off switch included only in said heater circuit, and manually-settable clock-controlled means for opening said switch at the end of a pre-set time interval, whereby upon the opening of said switch the heating current flow to the cathode heaters of said tubes is interrupted but anode current continues to flow for a substantial time at a gradually diminishing rate controlled by the thermal inertia of said indirectly heated cathodes, and the sound output of the radio receiver diminishes accordingly at a gradual rate.

References Cited in the file of this patent UNITED STATES PATENTS 1,881,357 Hayden Aug. 15, 1928 1,955,556 Moore Apr. 17, 1934 2,195,642 De Larm Apr. -2, 1940 2,439,732 Haydon Apr. 13, 1948 2,650,272 Gavigan Aug. 25, 1953 EI PA EN S 60,794 en ar -V--.-.-V-- API- 19 3 OTHER REFERENCES Publication: Motorola 1-8 Abridged Rider, vol. 11V, Motorola, page 13, Galvin Mfg. Co., copyright J. E. Rider, 1941, N.Y.C. 16, N.Y. Patent Oflice Library 

